I've just issued a pull request to remove all of the headers that include the opening comments and the licensing information from the individual source files in the yt-4.0 branch. This means that information will only be in the top-level repository, rather than in every file.
It is, evidently, bad practice to include the copyright -- which in any case has been out of date for several years anyway -- in each individual file, as it's included in the top-level directory. The leading comments in almost 100% of cases provided no useful information; it may be the case that they should be re-added, but as of present most are just copy/pasted.
I'm posting this here to make sure that it can be considered before getting merged, although having inspected the diff I believe there are no behavior changes. The question is basically if we want this boilerplate, frequently-outdated info in every file or not.
(PS the pull request is super long.)